A proton exchange membrane (PEM) fuel cell (PEMFC), alternatively called a polymer electrolyte membrane fuel cell, typically comprises an anode plate and a cathode plate separated by a membrane electrode assembly (MEA), typically with a gas diffusion layer (GDL) between each side of the MEA and its adjacent plate. The surfaces of the anode plate and cathode plate that face the MEA are shaped to provide a flow field for the reactant gasses, typically hydrogen and air. A PEM fuel cell stack comprises an assembly of fuel cells clamped between and end plates, end plate insulator and current collector at each end of the stack. In the stack, the anode plate and cathode plate of adjacent fuel cells are electrically connected and may be provided by a bipolar. The bipolar plate may be a unitary structure or an anode plate and cathode plate bonded together. Coolant flow fields may be provided between adjacent fuel cells, either between every pair of successive fuel cells or at some lesser interval, for example after every second to fifth fuel cell. The coolant flow fields may be provided within a bipolar plate, between abutting anode and cathode plates, or in a separate plate. Typically, there are also various holes through the thickness of the plates. These holes collectively define conduits through the stack (perpendicular to the plates) to transport reactants, reaction products, or coolant to or from the individual fuel cells. Seals are required between each flow field and the adjacent MEA. Seals are also required around the holes in the plates, and between the holes and their associated flow fields. Seals may also be required around coolant flow fields. Optionally, seals may also electrically insulate the anode plate and cathode plate of a fuel cell, or between adjacent bipolar plates. Due to the large number of seals and plates in a fuel cell stack, methods of making and assembling these components are constantly in need of alternatives to provide improvements or to be suited to selected manufacturing techniques and materials.
In U.S. Pat. No. 6,599,653, anode and cathode plates are molded from plastic composites that include graphite. The anode and cathode plates are made into a sub-assembly called a fuel cell unit. Each fuel cell unit also includes an insulation layer on the bottom of the anode plate, a bead of sealant between the anode plate and the cathode plate, and another bead of sealant on the top of the cathode plate.
The anode and cathode plate have aligned gates to facilitate the flow of a curable liquid silicone through the plates and grooves to receive the beads of sealant. A fuel cell unit is made by placing an anode plate and cathode plate on the floor of a mold with the anode plate spaced from the floor of the mold. Liquid silicone is then forced through the gates and into the space between the anode plate and the floor of the mold. When the silicone cures, the insulation layer and the two beads of sealant are formed as a unitary, contiguous mass. This mass bonds the anode plate and cathode plate together and provides an insulation layer and seal on opposed sides of the bonded plates.
U.S. Pat. No. 7,210,220 describes a sealing technique for fuel cells and other electrochemical cells. To provide a seal, a groove network is provided through various elements of a fuel cell assembly. One fuel cell assembly includes anode and cathode plates, MEAs and GDLs for several fuel cells, all clamped together between end plates, end plate insulators and current collectors. Insulating material is provided between the anode and cathode plates of each fuel cell to prevent shorts across the fuel cells. The insulation may be provided as part of an adjacent MEA (for example as a non-conductive flange bonded to the MEA), by a GDL which extends to the edge of the plate, or by using plates that are made non-conductive or covered with an insulator in these areas. A source of seal material is then connected to an external filling port and injected into the groove network. When the sealing material cures, it forms a “seal in place” that bonds and seals the fuel cell assembly elements. In an alternative embodiment, a Membrane Electrode Unit (MEU) is made which comprises 1 to 5 sealed in place fuel cells. At least one of the outer faces of the MEU has an outer seal. This outer seal is adapted to seal to another MEU. Typically, an outer face of the MEU is adapted to form a cooling chamber with the other MEU. A fuel cell stack is produced by assembling any number of MEUs with end plates, end plate insulators and current collectors.